“Canola” refers to rapeseed (Brassica spp.) that has an erucic acid (C22:1) content of at most 2 percent by weight (compared to the total fatty acid content of a seed), and that produces (after crushing) an air-dried meal containing less than 30 micromoles (μmol) of glucosinolates per gram of defatted (oil-free) meal. These types of rapeseed are distinguished by their edibility in comparison to more traditional varieties of the species. Canola oil is considered to be a superior edible oil due to its low levels of saturated fatty acids.
Although rapeseed meal is relatively high in protein, its high fiber content decreases its digestibility and its value as an animal feed. Compared to soybean meal, canola and oilseed rape meal contains higher values of dietary fiber and a lower percentage of protein. Because of its high dietary fiber, canola meal has about 20% less metabolizable energy (ME) than soybean meal. As a result, the value of the meal has remained low relative to other oilseed meals such as soybean meal, particularly in rations for pigs and poultry. Rakow (2004a) Canola meal quality improvement through the breeding of yellow-seeded varieties—an historical perspective, in AAFC Sustainable Production Systems Bulletin. Additionally, the presence of glucosinolates in some canola meals also decreases its value, due to the deleterious effects these compounds have on the growth and reproduction of livestock.
Canola varieties are distinguished in part by their seed coat color. Seed coat color is generally divided into two main classes: yellow and black (or dark brown). Varying shades of these colors, such as reddish brown and yellowish brown, are also observed. Canola varieties with lighter seed coat color have been widely observed to have thinner hulls, and thus less fiber and more oil and protein than varieties with dark color seed coats. Stringam et al. (1974) Chemical and morphological characteristics associated with seed coat color in rapeseed, in Proceedings of the 4th International Rapeseed Congress, Giessen, Germany, pp. 99-108; Bell and Shires (1982) Can. J. Animal Science 62:557-65; Shirzadegan and Robbelen (1985) Gotingen Fette Seifen Anstrichmittel 87:235-7; Simbaya et al. (1995) J. Agr. Food Chem. 43:2062-6; Rakow (2004b) Yellow-seeded Brassica napus canola for the Canadian canola Industry, in AAFC Sustainable Production Systems Bulletin. One possible explanation for this is that the canola plant may expend more energy into the production of proteins and oils if it does not require that energy for the production of seed coat fiber components. Yellow-seeded canola lines also have been reported to have lower glucosinolate content than black-seeded canola lines. Rakow et al. (1999b) Proc. 10th Int. Rapeseed Congress, Canberra, Australia, Sep. 26-29, 1999, Poster #9. Thus, historically the development of yellow-seeded canola varieties has been pursued as a potential way to increase the feed value of canola meal. Bell (1995) Meal and by-product utilization in animal nutrition, in Brassica oilseeds, production and utilization. Eds. Kimber and McGregor, Cab International, Wallingford, Oxon, OX108DE, UK, pp. 301-37; Rakow (2004b), supra; Rakow & Raney (2003).
Some yellow-seeded forms of Brassica species closely related to B. napus (e.g., B. rapa and B. juncea) have been shown to have lower levels of fiber in their seed and subsequent meal. The development of yellow-seeded B. napus germplasm has demonstrated that fiber can be reduced in B. napus through the integration of genes controlling seed pigmentation from related Brassica species. However, the integration of genes controlling seed pigmentation from related Brassica species into valuable oilseed Brassica varieties, such as canola varieties, is complicated by the fact that multiple recessive alleles are involved in the inheritance of yellow seed coats in presently available yellow-seeded lines. Moreover, “pod curling” is also a problem commonly encountered during integration of yellow seed coat color from other Brassica species, such as juncea and carinata. 
Very little information is available as to how much variability there is for fiber within dark-seeded B. napus germplasm, and no reports have been made of dark-seeded canola lines having been developed that contain reduced levels of anti-nutritional factors (e.g., fiber and polyphenolic compounds), and increased protein levels.